DESCRIPTION: This Proposal will address mechanistic aspects of gene therapy in experimental models of Parkinson's disease (PD) and explore ways to optimize and regulate catecholamine delivery in genetically modified cells initially in vitro. Attempts to alleviate end product inhibition will use mutated tyrosine hydroxylase (TH) molecules. The stability of Th protein expressed in non-neuronal environment as well as ways to improve that stability will be explored. Once biochemical issues are resolved, the principal investigator will generate a construct using the tetracycline-regulatable promoter (tet off). Both non-neuronal (fibroblasts) and neural precursor cell lines will be utilized, the latter of which the principal investigator hyprothesizes will provide a better environment to support expression of neuronal molecules and better properties in vivo after grafting in terms of integration and dispersion into the host brain. The efficacy of these approaches will be demonstrated biochemically by in vivo microdialysis and by following a non-drug-induced spontaneous behavior that reflects the skinesia of PD better than traditional drug-induced rotational behaviors.